PNNL-13501 - Pacific Northwest National Laboratory

Characterization of Global Gene Regulation by Tumor Necrosis Factor Alpha in Genetically
Defined Mice
Study Control Number: PN00019/1426
Brian D. Thrall, Kwong-Kwok Wong
The scientific goal of this project is to characterize gene regulation mediated by cell signaling pathways of broad
applicability to human biology and environmental health. This project will serve as a means to implement and focus the
Laboratory’s capabilities in mouse genomics (cDNA arrays and informatics), provide a focus and direction for the
integration of genomics and bioinformatics capabilities at the Laboratory, and build capabilities in support of our
biological sciences program.
Project Description
The cytokine tumor necrosis factor alpha (TNFα)
mediates a diverse range of cellular responses induced by
environmental agents, including apoptosis, cell proliferation,
and differentiation. TNFα-mediated signaling
pathways are known to be stimulated by a broad range of
environmental agents, including radiation, chemicals, and
pathogenic microbes. The cellular responses to TNFα are
tissue-specific, a reflection of cell-specific patterns of
genes regulated by the signaling pathways stimulated by
TNFα. This project will create a mouse-specific cDNA
microarray which will then be used to globally assess
these gene expression patterns regulated by TNFα in
isolated cells and in the whole animal. By understanding
these global patterns, tissue-specific differences in gene
regulation will be identified that will help integrate the
key signaling pathways that govern the cell-specific
responses to TNFα, in the context of the whole animal.
This information can then be extended to identify the key
molecular pathways that govern cell-specific responses
mediated by TNFα in response to exposure to environmental
contaminants such as radiation and chemicals.
Introduction
Among the cytokines that contribute to immune
responses, tumor necrosis factor alpha (TNFα) plays both
a major and early role in the inflammatory response. In
addition to a physiological role in immune function,
TNFα can also mediate direct cellular effects, including
apoptosis and mitogenesis, as well as promote
differentiation in a cell type-specific manner. Disruption
of the normal signaling pathways associated with
abnormal release and/or synthesis of TNFα is
hypothesized to contribute to a wide range of disease
states (reviewed in Luster et al. 1999). For example, an
essential role for TNFα in promotion of mouse skin
tumors has been independently demonstrated by two
studies (Saganuma et al. 1999; Moore et al. 1999).
Although the mechanisms for this are not understood, the
stimulation of clonal growth of initiated cells by TNFα
(secreted by tissue macrophages) is hypothesized. This
hypothesis is supported by in vitro studies that
demonstrate a promoting role of TNFα in mouse JB6
cells. Other pathological states linked to TNFα release or
deregulation include pathologies involving the immune
system, including autoimmune diseases, arthritis, multiple
schlerosis, and inflammatory bowel disease (Kollias et al.
1999). Evidence for a causative role of TNFα in the
etiology of lung fibrosis is particularly strong. For
example, TNFα released by phagocytic lung macrophages
may be responsible for a local induction of apoptosis after
exposure to particulate matter associated with air
pollution associated with energy-related facilities (Chin et
al. 1998). Stimulation of collagen and fibrinogen
synthesis in endothelial cells by TNFα is likely the initial
signal that leads to lung fibrosis after prolonged exposure
to particulate matter. Exposure to ionizing radiation also
stimulates TNFα release in lung cells. For example,
TNFα is a central mediator of the events leading to
radiation-induced lung fibrosis. Interestingly however,
low dose total body irradiation (0.2 Gy) has also been
associated with beneficial effects of TNFα, such as
inhibition of tumor cell metastasis (Hashimoto et al.
1999). The reasons for the pleitropic responses to TNFα
are unclear, but most likely reflect differences in the
signaling pathways induced and the global patterns of
genes regulated by TNFα in different cell types. Thus, to
understand the underlying basis for TNFα-mediated
effects, we need to evaluate the gene networks regulated
by TNFα in a global manner.
Biosciences and Biotechnology 45